They found the buyback program drove down firearm suicides by almost 80 percent, with no significant change in suicides that didn’t use guns. But the effect on homicides, while of “similar magnitude,” was less precise, they wrote — perhaps between 35 and 50 percent.

Two other studies, which Hemenway described as flawed, found the laws made little difference. But their design made it nearly impossible to find an effect, he argues.

The first, authored by members of the Australian gun lobby, highlighted the fact that before the law passed, the firearm homicide rate was already dropping. If it had continued on that track, they found, that would explain the entire change — showing the law made no difference.

The second study was more sophisticated. Authors searched for a shift in deaths in a single year that might be attributed to the law, and found their tests suggested the law didn’t “have any large effects on reducing firearm homicide or suicide rates.” Hemenway answers that the buyback occurred over two calendar years, in 1996 and 1997 — and the two-year drop was substantial. Gun homicides fell 46 percent.

Australian experts told us the science leans King’s way. But it’s not yet definitive.

“The truth is that gun homicide did decline substantially after the toughening of Australia’s gun laws and the massive gun buyback,” said Don Weatherburn, director of the New South Wales Bureau of Crime Statistics and Research. “The complication is that gun homicide was coming down before any of this. The academic debate is about whether the downward trend accelerated.”

His own view? That there’s some evidence that tougher gun laws reduced the homicide rate, but it is “far from conclusive.”

Paul Mazerolle, director of the Violence Research and Prevention Program at Griffith University in Brisbane, echoed that “more definitive work is required."

Some feel more certain the laws did their job.

An even messier question is whether similar laws would work in the United States. Australia doesn’t have domestic gun manufacturers — and has the benefit of being, you know, an island. Guns destroyed aren’t so easily replaced.

Our ruling:

King, urging his readers to support an American assault weapons ban, said that since Australia passed tough gun laws, “homicides by firearm have declined almost 60 percent.” The raw numbers back him up — but cause and effect are much peskier questions. Scholars we spoke with say the evidence leans King’s way, but is less than conclusive. That’s an important clarification. We rate King’s claim Mostly True.